With continuous progress of communications technologies, users are imposing an increasingly high requirement on voice quality. Generally, voice quality is improved by increasing bandwidth of the voice quality. If a signal whose bandwidth is wider is encoded in a traditional encoding manner, a bit rate is greatly improved and as a result, it is difficult to implement encoding because of a limitation condition of current network bandwidth. Therefore, encoding needs to be performed on a signal whose bandwidth is wider in a case in which a bit rate is unchanged or slightly changed, and a solution proposed for this issue is to use a bandwidth extension technology. The bandwidth extension technology may be completed in a time domain or a frequency domain. A basic principle of performing bandwidth extension in a time domain is that two different processing methods are used for a low band signal and a high band signal. For a low band signal in an original signal, encoding is performed at an encoder side according to a requirement using various encoders; at a decoder side, a decoder corresponding to the encoder of the encoder side is used to decode and restore the low band signal. For a high band signal, at the encoder side, an encoder used for the low band signal is used to obtain a low frequency encoding parameter so as to predict a high frequency excitation signal, processing is performed on a high band signal in an original signal to obtain a high frequency encoding parameter, and a synthesized high band signal is obtained based on the high frequency encoding parameter and the high frequency excitation signal; then the synthesized high band signal and the high band signal in the original signal are compared to obtain a high frequency gain that is used to adjust a gain of the high band signal, and the high frequency gain and the high frequency encoding parameter are transferred to the decoder side to restore the high band signal. At the decoder side, the low frequency encoding parameter that is extracted when the low band signal is decoded is used to restore the high frequency excitation signal, the synthesized high band signal is obtained based on the high frequency excitation signal and the high frequency encoding parameter that is extracted when the high band signal is decoded, then a high frequency gain is adjusted for the synthesized high band signal to obtain a final high band signal, and the high band signal and the low band signal are combined to obtain a final output signal.
In the foregoing technology of performing bandwidth extension in a time domain, the high band signal is restored in a condition of a specific rate, however, a performance indicator is deficient. It may be learned by comparing a frequency spectrum of a voice signal that is restored by decoding and a frequency spectrum of an original voice signal that, a restored voice signal sounds rustling and a sound is not clear enough.